(744e) CO2 Hydrogenation on Single-Site Heterogeneous Cobalt Catalyst

As the field of carbon dioxide capture and storage is expanding as a means of mitigating CO₂ emissions, transforming carbon dioxide into value added chemicals and fuels represents a more economically viable approach. Recently, various technologies of upgrading CO₂ have been explored, most notably electrochemical conversion and thermo-catalytic conversion. Typical catalysts for CO₂ hydrogenation consist of supported cobalt nanoparticles that have a size in the range of 5-15nm. However, such catalysts have several factors that can affect catalytic activity such as surface crystal faceting, particle size, or simply surface defects. As CO₂ hydrogenation has been shown to be a highly surface sensitive reaction, the surface structures of nanoscale catalyst can be prohibitively complex to establish a clear structure/activity relationship to guide the design of active catalyst.

In this study cobalt single site catalyst supported on silica, will be explored due to their highly uniform surface; allowing for definitive claims as to which surface species are responsible for specific reaction mechanisms. To characterize the structure and dispersion of the single-site catalysts techniques such as UV-vis, XAFS, XPS, TPR, and Raman were utilized under ambient conditions as well as under reductive environments to simulate reaction conditions. This understanding of the surface moieties coupled with their corresponding catalytic performance during CO₂ Hydrogenation we can discern how the transition between isolated atoms to small nanoparticles affects the reaction mechanism. In situ infrared spectroscopy will be used to follow the reaction mechanism as a function of surface structure based on the results from the characterization. Our results have shown that isolated atoms promote the preferential formation of CO via the RWGS reaction while small ensembles between Co²⁺(Td) and Co⁰ form both methane and CO, suggesting a change in reaction mechanism; which will ultimately be elucidated by this work.